Many different types of apparatus of this kind are known within the art. Pipetting apparatus and other types of apparatus for laboratory and/or clinical use, for instance dosing or metering devices for different types of analytic apparatus, will often comprise an arrangement which includes a dosing pump for taking different samples and reagents, and a washing pump which is used to wash away sample and reagent residues from the apparatus upon completion of the pipetting or analysis process. The washing pump is typically a plunger-operated pump or a syringe pump. A valve is required for connection of the washing tube when taking-up liquid, and correspondingly a valve is required for closing the take-up tube when pumping-up washing solution. In some cases, it has been possible to simplify the apparatus slightly, by using only one valve, in the form of a two-port two-position valve, which in one position connects the washing pump to a washing solution container, thus for taking-up washing solution, and in its other position connects the washing pump to the dosing pump and the take-up tube so that they can be washed with the washing solution.
An example of such an arrangement is described, for instance, in WO 93/12432. This publication describes an arrangement for washing a probe used in an analytic system. In the case of this known arrangement, the probe is washed with liquid and compressed-air or in some corresponding fashion in a reverse direction, i.e. liquid is passed to a two-way valve with the aid of a syringe pump, said valve being controlled to allow a mixture of liquid and compressed-air to pass through to the probe and therewith wash the same.
In addition to this type of arrangement being complicated by valves and valve control systems, the problem remains that the wash capacity of the washing pump is naturally restricted to the volume of washing solution that can be drawn up by the pump in one working stroke. Although it is feasible to suck-up and inject washing solution repeatedly during a washing process, such a procedure is particularly time-consuming.
Another solution to the problem is described in the British Patent Specification GB 1,502,77. This publication describes a device for taking-up and analyzing a liquid in which a peristaltic pump is used to move liquid through the device. By liquid is meant here the sample, possible reagent and washing solution. In the case of this device, the sampling probe is submerged into washing liquid which is taken-up through the probe orifice so as to wash the device. The sample and the washing solution thus pass through the device in one and the same direction and through one and the same pump, which places high demands on adequate washing of the device, among other things. The use of the peristaltic pump to take-up samples means that the amounts of sample that can be taken are greatly dependent on the specific construction of the pump.